An apparatus for applying a predetermined process treatment, such as an etching process or film forming process, to a substrate to be treated, such as a glass substrate (for example, a liquid crystal substrate) or semiconductor wafer (hereinafter, referred merely as “wafer”) is provided with a treatment unit, which includes a treatment chamber connected to a load lock chamber for applying a predetermined treatment to the wafer, for example. Further, the apparatus is provided with a cassette container for storing an untreated wafer transferred into the apparatus or a treated wafer transferred outside the apparatus, and a transfer chamber having a transfer system for passing and receiving the wafer between the load lock chamber etc. In such a transfer chamber, a loading and unloading gate is provided respectively between each of the load lock chamber or cassette container, and the wafer is passed and received between the load lock chamber and cassette container through these loading and unloading gates, for example.
In such an apparatus, as the cassette container storing untreated wafers is set to the cassette table, the untreated wafer is removed from the cassette container by the transfer system in the transfer chamber through the loading and unloading gate to the cassette container, and the wafer is passed onto the treatment unit. This untreated wafer is transferred into the load lock chamber through the loading and unloading gate to this load lock chamber. Thereafter, the wafer is transferred to a treatment chamber from the load lock chamber and a predetermined treatment is applied. The wafer that had been treated in the treatment chamber is returned to the load lock chamber from the treatment chamber. The transfer system in the transfer chamber receives the treated wafer returned to the load lock chamber and returns it to the cassette container.
In the transfer chamber, the transfer of untreated wafers and treated wafers is performed by the transfer system in this way, the operation, such as, wafer transfer etc., causing particles (for example, dust, dirt, fouling, reactive product etc.) to be present in the transfer chamber. These particles may adhere on the surface of the wafer during the transfer, and if the wafer is processed with the particles adhered, this may lead to a decrease in through put. For example, in an etching process, excess etching may occur because of the particles adhered on the surface of the wafer act as a mask, and also in a film forming process, the quality of film may deteriorate because the film is developed with a particle adhered on the surface of the wafer acting as a core. For this reason, in a transfer chamber, particle removal filters, such as, HEPA (High Efficiency Particulate Air) filter or ULPA (Ultra Low Penetration Air) filter, are provided and a predetermined gas, for example an inert gas, such as N2 gas, or air, is cleaned by these filters and the down flow of clean gas described above is formed in the transfer chamber.
In such a down flow, for example, it is common to provide a blower fan and filter on the upper side, as well as an exhaust opening on the lower side of a chamber where down flow is to be formed, and form a down flow of gas by taking clean gas into the chamber from the upper side through the filter by the blower fan, blowing the clean gas downward, and exhausting it from the exhaust opening of the chamber. For an example, refer to Japanese Patent Application Publication No. 11-63604.
By the way, in the transfer chamber, in which a plurality of loading and unloading gates are installed in a horizontal direction, the transfer system is also provided movably in a horizontal direction so as to exchange wafers through each of the loading and unloading gates. Further, the speed of down flow of the clean gas formed in the transfer chamber is adjusted to a constant speed (for example, in a range of 0.25 to 0.35 m/s), thus, without adhering to the surface of the wafer that is being transferred, the particles floating in the chamber can be exhausted outside of the chamber after guiding to the lower side of the transfer chamber along the down flow by transferring the wafer horizontally in this down flow.
However, depending on the configuration of transfer chamber, there may be a case where the plurality of loading and unloading gates are arranged in different heights and the size of the plurality of loading and unloading gates in a height direction is different. For example, in the case of a transfer chamber connecting a plurality of load lock chambers, the loading and unloading gate for each of the load lock chambers may be arranged vertically. Further, in the case of a transfer chamber capable of exchanging wafers between the cassette container, which contains a plurality of wafers arranged in a height direction, the loading and unloading gate with a size larger in the height direction may be provided so that the transfer system can access all of the wafer arranged vertically in that cassette container.
In such a transfer chamber, the transfer system is configured to move not only in a horizontal direction, but in a vertical direction so as to transfer the wafer up and down, and there are cases where the wafer is transferred downward in the same direction as the down flow. However, with the conventional technique, there has been an issue of not being able to sufficiently prevent the adherence of particles to the surface of the wafer because the speed of down flow is maintained at a constant speed and the relative speed of down flow against the wafer transferred downward is decreased depending on the speed of the downward transfer. Especially when the descent speed of the wafer is faster than the speed of down flow, up flow is formed temporarily around the wafer, thus the floating particles are likely to adhere on the surface of the wafer.
Further, in many cases, the gas used in a treatment remains on the surface of the treated wafer that has been applied with a predetermined treatment in the treatment chamber, thus the gas of impurity (out gas) adhered on the surface of the wafer is transferred into the transfer chamber along with the wafer when the wafer is transferred into the transfer chamber as it is. Normally, such out gas is exhausted out of the transfer chamber along the flow of down flow in the transfer chamber while transferring in the transfer chamber. However, if the speed of the down flow is maintained at a constant speed even when the amount of out gas from the treated wafer is large, a high degree of cleanliness in the transfer chamber may not be maintained because such an out gas can not be exhausted entirely and remains on the wafer, or is scattered in the transfer chamber. In this way, because particles attributed from the out gas are adhered on the surface of the treated wafer or an untreated wafer, which is consequently transferred into the transfer chamber, when the degree of cleanliness in the transfer chamber is decreased, there may be a possibility of decreasing the through put.
Considering the descent speed of the wafer in the transfer chamber or the amount of out gas from the treated wafer, a method, in which the speed of down flow is consistently maintained at high speed, can be considered. In this case, however, not only the speed of down flow is unnecessarily maintained to a high speed even in a case when there is no need to increase the speed of down flow, such as when transferring the wafer horizontally or transferring the untreated substrate, but also increasing the power consumption for forming the down flow or shortening the life of expendable parts. Therefore, this method is not appropriate due to these disadvantages.
The present invention has been made considering issues described above and an object is to provide a substrate transfer apparatus and method for controlling down flow that are capable of preventing particles from adhering to the surface of a substrate in a transfer chamber by adjusting the speed of down flow formed in the transfer chamber with an adequate timing.